Biochemistry : Nucleic Acid Degradation

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #1 : Nucleic Acid Degradation

Which of the following statements about restriction enzymes is true?

Possible Answers:

Reverse transcriptase is a DNA polymerase which creates new strands from 3’ to 5’

None of these answers is true

Restriction enzymes can only cut bacterial DNA

Restriction enzymes act at RNA mutation sites, to create a covalent bond which links two adjacent exons after an intron sequence is excised

Restriction enzymes are endonucleases which recognize a restriction site and cut DNA within or around this site

Correct answer:

Restriction enzymes are endonucleases which recognize a restriction site and cut DNA within or around this site

Explanation:

Reverse transcriptase synthesizes DNA in the 5' to 3' direction, using RNA as a template (hence it is the reverse of transcription). Restriction enzymes act only on DNA, not RNA, and they can cut bacterial as well as viral DNA—indeed, they can provide protection against viruses—and are found in archaea. Restriction enzymes can recognize specific sequences of nucleotides at restriction sites and cut DNA at these sites. Restriction enzymes do not create covalent bonds between adjacent exons after intron excision, rather this is done by tRNA splicing ligase. 

Example Question #50 : Nucleic Acid Structures And Functions

What is the role of xanthine oxidase?

I. The enzyme xanthine oxidase converts hypoxanthine to xanthine and, also, xanthine to uric acid.

II. Xanthine oxidase is involved in purine (nucleotides like adenine, guanine) degradation.

III. In diseases where there is a high production of purines, the enzyme's products (uric acid) can cause gout.

IV. Gout medication is designed to target xanthine oxidase.

Possible Answers:

I and IV

I, II, and III

I, II, III, and IV

I and II

II, III, and IV

Correct answer:

I, II, III, and IV

Explanation:

Xanthine oxidase is an enzyme important in purine catabolism. Nucleotides from DNA degradation are metabolized to uric acid by xanthine oxidase.In diseases with high levels of nucleotide production, uric acid levels are also high and produce symptoms of gout (uric acid is deposited abnormally in tissues). Gout is treated with inhibitors of xanthine oxidase such as allopurinol, reducing the levels of uric acid and the symptoms of gout.

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